In the near future an increasing demands of communication over wide distances, especially for example between continents will be needed. Hence, infrastructures, like sea cables, connectors and penetrators linking sea cables and modules, e.g. subsea modules, like transformers, pumps etc., that are located and operated error proof subsea will be essential. Some subsea units (pumps, switch gear, VSD, etc.) require electrical connections through a wall to carry high currents at high voltages. These kinds of connectors are often referred to as penetrators. These penetrators must insulate the walls of the module from the high voltage cores of connected cables and be able to withstand these voltages without breakdown or partial discharge. Furthermore, if the unit does not have internal pressure compensation the penetrator will have to withstand high differential pressures. Another issue that penetrators face is that, if they are connected to an external cable, it is possible that a large pulling force may accidentally be applied to the conductive core.
It is for example known to manufacture connectors/penetrators by moulding a plastic insulation layer (normally Epoxy or PEEK) onto a solid copper core. The copper core then provides the conduction path and the plastic insulates the module walls from the high voltages and provides the mechanical strength to withstand the differential pressures. The downsides of this method include that in case of an applied pulling force the moulded connection between the insulation and the conductive component may break. This may cause the connector/penetrator to leak or to expose the high voltage core to fluids which may degrade its performance. With an over-moulded insulation there are other issues like: The plastics have a much greater coefficient of thermal expansion than the copper core. As the copper cores are solid copper this can lead to differential thermal expansion issues. This in turn can lead to high stresses and weakening of the plastic during the curing/heat treatment of the plastic and when the penetrator is exposed to varying temperatures. The moulding method does not lend itself to engineered seals. The sealing between the plastic and the copper core is achieved by bonding the plastic to the metal. However the plastic can be difficult to bond to the metal reliably and the differential thermal expansion issues (mentioned above) can break these bonds, with the same disadvantageous results as stated above. Moreover, the over-moulding process can introduce impurities, weaknesses or air voids in the plastics which can reduce the electrical performance of the connector/penetrator.
It is further known for example from US 2013/0183853 A1 to use a ceramic bushing with a two part copper core with a sliding contact in the middle. The used construction allows an axial movement of the parts of the copper core relative to the ceramic bushing as well as for the longitudinal differential thermal expansion as the length of the copperwork can change without applying extra stress on the bushing. It does however still have disadvantages to do with the sealing method. The seal will be achieved by a metal to metal seal (through welding/brazing etc.) between the conductor and a metallic plating on the ceramic insulator. Not only is this method relatively complicated to reliably achieve a good seal it still relies on metal to insulator bonding for the seal. This will still be vulnerable to differential thermal expansion effects and could be damaged by an accidental pulling force on the parts of the copper core or with thermal cycling. The other disadvantage is that if the seal at the pressurized end does fail/leak for any reason (i.e. through damage due to differential thermal cycling, poor manufacturing, accidental pulling loads or just diffusion though a weakness in the sealing method) it will cause the pressure to build up in the volume between the conductor and insulator. This will load the penetrator in a way that it was not designed for and as the two copper ends are not fixed together, will eject the copper in the non-pressurised end from the penetrator, potentially causing catastrophic failure.